A known combustion control apparatus for a diesel engine is disclosed, for example, in Patent Document 1. The known control apparatus uses a cylinder pressure sensor to detect ignition timing of fuel. Fuel injection timing, an EGR ratio, or the like is then corrected based on a difference between an actual ignition timing detected and a target value. A technique of such a known control apparatus can control combustion of the diesel engine, while inhibiting negative effects associated with a change in a cetane number as an ignitability index value of fuels.
Including the above-referenced document, the applicant is aware of the following documents as a related art of the present invention.    [Patent Document 1] Japanese Laid-open Patent Application Publication No. Hei 11-107820    [Patent Document 2] Japanese Laid-open Patent Application Publication No. 2004-239229